This case fascinates me. I know many of you have way more knowledge of this case than I do, but here are my amateurish observations....
1) When Brandon left his car, he was going North towards Bronte/Abilene. If you look at the map, Abilene is the biggest city anywhere close to that area and Brandon is alerting the 911 operator that he's headed on 277 towards Abilene. That would also explain why he told his brother's gf that he was ten minutes "up" the road because his brother was coming from the South.
2) When you look at the Google map/Google Earth images, I think that the business/structure/home on the West side of the road has something to do with this. I think that's where he either encountered the trouble (maybe going for help) or that's where he was chased. If you look just north of the structure, there's a wide open field. Across the street there's a heavily wooded area. It's always bothered me that he said something about heading towards Abilene "on both sides." If you look at the overall map and what he's saying, I think he's trying to tell the dispatcher that someone got chased up into the woods on the other side of the road (the East side, which is much more heavily wooded). The West side of the road is a big, open field. It would make sense that maybe he can see/hear what's going on just on the other side of the road. Sticking close to the road could also explain the sounds in the background of the recording. Being on the West side of the road would've also put Brandon at a tactical disadvantage because it looks like there's little to no cover on that side of the road for several hundred yards, so he was likely moving/running in the wide open where even if someone was on the other side of the road, they could find him pretty easily. Not a lot of places to hide from a gunshot.
3) I think Brandon ultimately ended up close to the Colorado River than people think and may have been dumped somewhere in or around there. The family thinks that the final ping on his phone close to the river was non-specific because the range of the ping was up to three miles. I just have a gut feeling that when Brandon started running for whatever reason, he was trying to make it to Bronte and never got there. There's virtually no houses or places of sanctuary on that road other than the structure that I mentioned above. If that's where he ran into trouble, he may not be able to visualize another house from where he was until/unless he crossed the river. People tend to run to what they know when they get in trouble. For him, I think he was trying to get to Bronte or at least close enough to the river that he could seek cover on his side of the road without veering too far off the road in case his brother came to save him.
Just my amateur thoughts. I wish they'd find this guy. Feel terrible for all involved.